1. Field of the Invention
The present invention is directed to an X-ray diagnostic apparatus for a tomosynthesis, and in particular to an apparatus of the type employing a reference object in the radiation beam proceeding from the radiation emitter.
2. Description of the Prior Art
PCT application WO 93/22 893 discloses a method with which it is possible to reconstruct an exposure of an examination subject without the projection angle .alpha. and the geometrical arrangement of the radiation emitter and radiation receiver and the focal plane being known. According to this method, a reference object of radiation-absorbing material having a known size and a known spacing from the radiation receiver is provided in the region of the radiation receiver, this reference object being projected onto the radiation receiver in every individual projection. The geometrical arrangement and the two-dimensional projection angle .alpha. for each individual projection can be determined on the basis of the two-dimensional spatial imaging of the reference on the radiation receiver.
A holder for positioning a radiation emitter of an X-ray diagnostic apparatus for tomosynthesis is disclosed in German OS 44 14 689, corresponding to U.S. Pat. No. 5,598,454. A bracket is coupled to the holder, at which --as viewed in the radiation propagation direction --a spherical reference object is arranged in front of the examination subject and a radiation receiver is arranged behind the examination subject. The spacing of the radiation from the reference object and from the radiation receiver, as well as the angle .alpha. of a ray beam emitted by the radiation emitter relative to a reference axis of the holder mechanism, are prescribed by the holder. It is also known to arrange the radiation source so as to be adjustable in a housing to which a positioning means for the reference object and the radiation receiver can be coupled.
In such known tomosynthesis systems, because the reference object is disposed in front of the examination subject and is mounted on a bracket connected to the holder for the radiation receiver, the reference object can constitute a nuisance or an impediment in setting up the apparatus and conducting the examination.